1. Technical Field of the Invention
The present invention relates to a light emitting device such as an LED (Light. Emitting Diode) or the like, a module (light emitting module) using a light emitting device, a lighting apparatus loaded with a light emitting module, and further an image projection apparatus loaded with this lighting apparatus.
2. Description of the Related Art
In recent years, various lighting apparatuses using an LED module have been developed. There have been demands imposed on such lighting apparatuses for achieving higher luminance and downsizing. Thus, lighting apparatuses disclosed in patent documents 1 and 2 attempt to achieve higher luminance by using a light emitting module loaded with a plurality of LEDs.
[Patent Document 1] U.S. Pat. No. 6,547,400
[Patent Document 2] U.S. Pat. No. 6,318,863
As shown in FIG. 21A, an LED module 171 of the lighting apparatus disclosed in patent document 1 is loaded with a plurality of LEDs 181 each provided with a shell type cap 182. In such an LED module 171, the shell type cap 182 does not actually emit light but just an LED chip included in the shell type cap 182 emits light. Thus, loading a plurality of LEDs 181 upsizes the LED module 171 and also hardly achieves sufficiently high luminance.
Patent document 1 also discloses a lighting apparatus loaded with an LED module 171 having a plurality of LED chips 184 arranged on one substrate 183 as shown in FIG. 21B. However, when a current flows through the LED module 171, the temperature of the substrate 183 increases due to heat generation of the LED chip 184 caused by the power distribution. In particular, due to the arrangement of a plurality of LED chips 184 on one substrate 183, when one of LED chips 184 is heated by the power distribution, the heat is conducted to other LED chips 184. As a result, the junction temperature is extremely likely to increase, whereby the luminance of the LED module 171 does not become high.
Considering the temperature-related problem, the lighting apparatus 170 of patent document 2 and shown in FIG. 22 is loaded with an LED module 171 using a plurality of low-power LEDs 181 to thereby achieve higher luminance. In particular, this lighting apparatus 170 has integrator rods 172 in correspondence with the respective LEDs 181, thereby achieving higher luminance.
However, due to the low power property of the LED 181, a relatively large number of LEDs 181 needs to be provided inevitably, further requiring the integrator rods 172 in accordance with this number. Thus, this lighting apparatus 170 is extremely upsized, and faces difficulty in simultaneously satisfying demands for achieving both higher luminance and downsizing.
There is one referred to as a power LED capable of ensuring a brightness of several tens of lumens (1 m) to one hundred lumens or more with a relatively large power of several watts (W). Thus, use of an LED module using such a power LED may provide a lighting apparatus which ensures high luminance. However, with only introduction of a large electric power, the LED module fails to ensure high luminance.
The reason for this failure of the LED module to ensure high luminance is as follows. An increase in a current to be distributed in order to introduce a power of several watts heats up the LED chip, thereby causing an increase in the junction temperature whereby the luminance of the LED chip (and thus the LED module) does not become high. Note that the junction temperature characteristic depends on heat dissipation characteristic of the LED module (in another word, it depends on the heat dissipation characteristic of the LED). That is, favorable heat dissipation characteristic of the LED module results in a low junction temperature.